Transition from and to glass tubing

There are various options for bonding different materials to one another. An everyday example is the garden hose. The hose is normally pushed into a metal sleeve that is then clamped tight. This generally creates a tight water conduit that transports water from one end to the other. However, this connection is certainly not airtight. If you tried to create a vacuum in the hose you would surely be successful, but it would equalize after only a few hours. How long the vacuum is maintained doesn’t usually depend so much on the hose used as it does on the tightness of the transition between the materials; i.e. between the rubber hose and the metal sleeve. Significantly tighter than any rubber hose pushed into a metal sleeve is a connection in which glass is used to directly fuse glass to metal. This creates connections that can sustain a vacuum for several years.
Of course, this doesn’t work with just any glass; certain prerequisites must be fulfilled. The make-or-break parameter is the thermal expansion of both materials. Glass is typically hot worked at 1,000°C and above, so the connection is subject to great temperature fluctuations. The connection is furthermore exposed to temperature fluctuations during use over a long period. Both cause the two materials to contract when cooled and expand when heated. The idea behind glass to metal seals is to combine types of glass and metals or alloys so that they both have approximately the same thermal expansion in the relevant temperature range. Glass is a brittle material and can easily break as soon as metal exerts tension on its surface through higher or lower expansion. If the expansion is similar or identical, a stable connection can be established.
Such connections have already been successfully established for different combinations. For example, specific types of lamps such as flash lamps, used for instance in hair removal, already employ direct seals between their tungsten electrodes and borosilicate glass such as Glass 8487 from SCHOTT. Also lamps with molybdenum electrodes, such as those used in the headlights of cars, are reliably sealed for the fused-in gas mixture in the bulb by fusing with aluminosilicate glass SCHOTT Glass 8252 and 8253.
Finally, there are special alloys, commonly known under the name “Kovar”. In many electronic components they form the transition to an electric, highly insulating borosilicate glass such as SCHOTT Glass 8250. These can often be found in a variety of X-ray sources applied in radiology, such as in computer tomography (CT). Here, glass seals off the vacuum chamber for generating X-ray radiation, while at the same time providing electric insulation for the metals and electrodes exposed to high voltage.
Are you looking for a suitable fusing glass that also combines other features? Then visit our Glass Tubing Explorer and combine any of the features to find the glass most suited to your needs!

Here you'll find infomation about graded seal glass rods formerly produced by Transition Glass Products TGP

Bonding glass and ceramics or other materials

When someone wants to bond glass and ceramic they can use Glass 8436.

For bonding materials with high thermal expansion such as Dumet or platinum and certain types of steel, AR-Glass® is the right choice, since it has a high expansion coefficient.

Glass types 8228, 8229 and 8230, used primarily in the field of electronics, provide high resistance to temperature change and provide fusing transition to quartz thanks to their low expansion coefficient.

If you need to bond borosilicate glass 3.3 such as DURAN® to Kovar or Vacon10, you need, in this order, our transition glass 8448, 8449 and 8447. Mit der Glasart 8448. With Glass type 8448 you can produce a material transition from borosilicate glass 3.3 to Tungsten.
Use the glass spectrum on our Glass Tubing Explorer to find information on glasses suitable for fusing.
Selection Filter features in Glass Tubing Explorer:
Selection „Sealing glasses“:
If you are not sure which type of glass is right for your application or whether what you want to do can be realized with glass - Ask our glass specialists!
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